Alarm circuit with false warning prevention



July 20, 1965 J. E. LINDBERG ALARM CIRCUIT WITH FALSE WARNING PREVENTION Filed April 30, 1

3 Sheets-$heet 1 28 VOLTS D. 6.

INVENTOR. JOHN E. L/NDBE/PG v J. E. LINDBERG ALARM CIRCUIT WITH FALSE WARNING PREVENTION Filed April' 30, 1964 3 s-Sheet 2 INVENTOR, DBERG (9W,UM,M

ATTORNEYS July 20, 1965 J. E. LINDBERG ALARM CIRCUIT WITH FALSE WARNING PREVENTION Filed April 30, 1964 3 Sheets-Sheet 3 INVENTOR. JOHN E. l/IVDBE/"PG BY v AT TOR/VEYS United States Patent 3,196,423 ALARM CIRCUKT WITH FALSE WARNING PREVENTION John E. Lindberg, Alamo, Caiif. (1211 Upper Happy Valley Road, Lafayette, Caiif.) Filed Apr. 30, 1964, Ser. No. 363,836 9 Claims. (Cl. 340-413 This invention relates to improvements in warning and alarm circuits. More particularly, it relates to improvements in circuits such as those used for detection of fires in airplanes and elsewhere.

Fire detection circuits and some other types of warning circuits heretofore in use have been prone to give false alarms. Recent statistics indicate, for example, that, on the average, two false fire warnings per day occurred on the commercial airlines in the United States alone. Each false warning was liable to cause a fatal crash, and several of these occurred each year in recent years. Even when the plane and passengers were saved, each false fire warning required immediate remedial action such as dumping excess fuel down to the allowable landing weight and landing as soon as possible, and the resultant disruption of the schedule, the costs of landing, taking off again, and obtaining clearances, and other expenses resulting from this false warning have been estimated to average more than $20,000 additional expenditure per false fire warning.

One object of the present invention is to provide a fire detection circuit that will not give such false fire warnings.

A leading cause of the false warnings in fire detection systems has been the presence of moisture or electrolytic solutions (some of which are formed merely by condensation or atmospheric moisture coming into contact with fire detector systems using salts or having soluble salt deposits on their surfaces), and the present invention eliminates this cause of false warnings. The invention obtains such favorable results that the critical parts of the electrical system can even be immersed in an electrolyte such as salt water, even with the terminals intentionally exposed, and yet there will be no false fire warning. Moreover, in many instances, the system will still give a true warning when there is a fire, and in those instances in which it is not in condition to give a true Warning, a circuit breaker is opened, thereby bringing the situation to the attention of the responsible person without causing a false alarm.

I have, in a previous patent application, Serial No. 179,538, filed March 12, 1962, now Patent No. 3,154,772, described a system in which false warnings were eliminated by employing low voltages and relatively high am perage in a manner that acted to passivate the exposed electrodes. This passivation cannot be achieved with high-voltage systems or with low power systems. This excellent system had one important disadvantage, namely, that it required a low-voltage power source. This meant either the incorporation of special batteries or additional or special transformers and converters. On airplanes, for example, where the electrical system is a 28-volt direct current system it was expensive to convert the supplied power to a 3-volt or'6-volt system. Hence, another object of the present invention is to provide a no-false-warning system capable of operating on 28-volt DC. electrical circuits and, in fact, on even higher voltage.

Another object of the invention is to provide a low cost no-false-warning alarm system.

Other objects and advantages of the invention will appear from the following description of a preferred embodiment thereof.

In the drawings:

FIG. 1 is a circuit diagram of a system embodying the principles of the invention, some of the parts being shown 3,196,423 Patented July 20, 1965 in diagrammatic form and some in representational form, with no attempt at scale.

FIG. 2 is an enlarged view in section taken along the line 22 in FIGS. 1 and 3 with a portion of the shunt electrode washer broken away and shown in section.

FIG. 3 is a view in section taken along the line 33 in FIG. 2.

FIG. 4 is a perspective view of the shunt electrode washer.

FIG. 5 is a circuit diagram of a modified system employing an ungrounded circuit with a return wire.

The circuit of FIG. 1 has a source of (for example) 28-volt direct current having a ground 11 and a positive pole 12 connected by an insulated lead 13 to a circuit breaker 14 of standard structure. The circuit breaker 14 is connected by an insulated lead 15 to a connection socket 16, shown in more detail in FIG. 3. The socket 16 comprises a metal housing 17 and two metal, electrically conductive receptacle contacts 18 and 19 insulated from each other and from the housing 17 by insulating material 29. The insulated lead 15 is soldered to or swaged in the contact 18, and an insulated lead 21 is soldered to or swaged in the contact 19.

The contacts 18 and 19 serve as the female receptacles of the socket 16 and are connected respectively to prongs or pins 22 and 23 of a responder 25, which may have the form shown in my patent application Serial No. 86,252, filed January 26, 1961, which comprises a movable metal diaphragm 26 brazed between two metal plates 27 and 28 and moved by gas pressure against an electrode 31) for actuation of the warning circuit. The electrode is insulated from the plate 28 by an insulator 31. The diaphragm 26 is thus the movable element of an electrical switch which is thrown by pressure, and the electrode 30 is the stationary pole against which and away from which the diaphragm (switch arm) 26 moves. The prong or pin 23 is brazed to the plate 28 and is therefore electrically connected to both plates 27 and 2S and to the diaphragm 26. The gas pressure used to actuate the responder 25 is governed by a sensor tube 32 containing gas or a material such as zirconium hydride which releases large quantities of gas when a critical temperature is passed, or both. The sensor tube 32 is flexible and is disposed along a desired path in the fire area. The interior of the sensor tube 32 and the diaphragm chamber 33 provide a closed, hermetically sealed volume.

The responder 25 is contained in a metal housing 35, being insulated from it by an insulator 36 of suitable structure. The sensor tube 32 is also insulated from the housing by an insulating tube 37. Preferably, a crook 38 in the sensor tube 32 is provided, surrounded and supported by the insulator 36, to help guard the tube 32 from being pulled out of the responder 25, to the plate 27 of which it is brazed Via a metal tube 39.

The housing 35 protects the responder 25 from damage and is itself grounded, as by attachment to the frame 40 of the airplane. It provides a receptacle 41 that receives the socket 16, and an aligning rib 42 engages a recess 43 in the socket 16 to assure alignment and proper polarization, so that the right lead 15, 21 is aligned with and is put into contact with the right prong 22, 23.

The lead 21 is shielded by a metal shield 44, preferably of woven or braided wire, and the shield is grounded at 45. The lead 21 goes through warning lamps. 46 to ground at 47. There may also be audible warning means as in my patent application Serial No. 367,273, filed April 20, 1964, a division of Serial No. 239,440, filed November 23, 1962.

The far end of the sensor tube 32 is provided with a tail connection means 50, which is grounded to the frame 40 and a tail connecting lead line 51 is provided. This line 51 is shielded by a grounded shield 52 and leads to a test switch 53 in the pilots or engineers control. The test switch is connected by a lead 54 through a circuit breaker 55 to the main line 15.

In the present invention 1 provide, in addition to all the foregoing, a thin highly conductive metal disc 60' which acts as a shunt electrode. The disc 60 has two openings 61 and 62 that are disposed to encircle and to be spaced from the prongs 22 and 23. A recess 63 mates with the aligning rib 42. The periphery 64 is made large enough to assure good electrical contact with the grounded housing 41, and it may be brazed or welded to the housing 41. A web 65 separates the two holes 61 and 62. This seemingly simple disc 60 safeguards the entire device against false warnings due to electrolytic shorting across the pins 22 and 23.

If any electrolyte, such as might result from water condensing in the receptacle 41 and dissolving salts carried by the air or otherwise, were in the receptacle 41, then it might develop a conductive path between the two terminals 22 and 23 of the responder 25. This might ordinarily cause a false warning, because if the lead 15 were connected to the pin 22 and if electrolyte connected the pin 22 to the other pin 23 and thereby to the lead 21, then the lamp 46 would be lighted and a false warning would be given. Although the housing 35 is grounded, the electrolyte current path between the prongs 22 and 23 is normally sufficient to pass electricity in quantity across the lines 15 and 21. However, in the present invention, the presence of electrolyte will not give a false warning. Instead, the current passing between the terminals 22 and 23 or tubes 18 and 19 is shunted to the disc 60, since the web 65 is closer to either prong 22, 23 than they are to each other and is closer to either tube 18, 19 than they are to each other. Also, the disc 60 is directly connected by its periphery 64 to the housing 35 and thereby to ground, i.e, the other side of the power-supply battery 11. The grounding being obtained by the actual airplane frame 40 ground is the same ground which is used to complete other circuits in the airplane, the same one to which the shieldings 44 etc. are grounded and to which the other side of the lamps 46 are grounded, and of course this is the same ground as the ground 11 for the power supply battery 11.

If the electrolyte passes enough current to create a very low resistance path to ground, then the 28-volt power source will be grounded, and the circuit breaker 14 will therefore be thrown, calling the situation to the attention of the operator. If, on'the other hand, the resistance path to ground is of relatively high resistance, it will be of substantially lower resistance than that between the two terminals 22 and 23, since the web 65 of the disc 60 is closer to the terminals 22 and 23 than they are to each other, and during this time, if the power loss is not enough to actuate the circuit breaker 14, that means that sufficient power remains so that if the diaphragm 26 is moved against the electrode 30, the lamps 46 will become lighted if there is (and only if there is) an actual fire condition. The diaphragm 26 cannot be moved against the electrode 30 unless the gas pressure.

moves it there.

The grounded shielding 44 is also important. If the two insulated leads and 21 are brought out together and if there is any exposure of the power lead 15, its current will not pass to the lead 21 but will pass immediately through the shielding 44 to ground, and the circuit breaker 14 will be thrown. There will not be passage of current to the shielded line 21.

The test switch 53 is used to test the continuity of the sensor 32 and the continuity of the electrical circuits. Whenever it is operated, the lamps 46 will necessarily be lighted so long as the switch 53 is closed. By shielding the lead 51 from the tail connector 50 to the test switch 53, protection of a similar nature to that afforded by the shielding 44- is given, in that if this tail connector lead 51 is brought back in a bundle along with the main line 15, the effect of fraying of the main line cable 15 will be to ground it and open the circuit breaker 55. Indication i given by opening of the circuit breaker 55 so that the operator knows that repair is needed.

FIG. 5 shows an ungrounded circuit having a power supply 70 which may be AC. or DO. A lead '71 goes to warning devices '72, and a lead '73 goes to the receptacle contact 18. A lead 74 from the receptacle contact 19 goes to the other side of the warning device 72. A lead 75 goes from the housing 35 to the lead 71. If (by accident) an electrolyte 76 gets in between the socket 116 and the pins 22 and 23, as shown by way of example (it is, of course, not introduced purposely) it tends to short across the prongs 22 and 23, but this tendency is defeated by the shunt disc 60, which, in that event, returns the current from lead 73 through the leads 75 and '71 direct to the power source 74 and prevents this shorting from lighting the warning device 72. Basically, the circuit of FIG. 5 is a simplified version of the circuit of FIG. 1 to illustrate the principles inherent therein.

To those skilled in the art to which this invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the spirit and scope of the invention. The disclosures and the description herein are purely illustrative and are not intended to be in any sense limiting.

I claim:

1. In an alarm system having a normally open electrical circuit with a pair of conductors connected to a first connector,

means for closing said circuit under true-alarm conditions,

a source of electrical power having a first side'and a second side,

an electrically actuated warning device, having a first side connected to the first side of said power source and having a second side, and

a pair of insulated wires connected to a second connector, said first and second connectors being joined to each other by a plug-socket-connection to each other, one said wire being connected to said second side of said source and the other said wire being connected to the second side of said warning device,

the combination'therewith of:

an electrically conductive electrode interposed in said plug-socket-connection between said two connectors and spaced from the conductors thereof and having a portion in between and spaced from said connectors and electrically connected to the first side of said power source, so that should electrolyte be present in said plug-socket-connection, said electrode passes di- 7 rectly to power source such current as flows through said electrolyte rather than causing a short circuit between the pair of wires and rather than causing actuation of said warning device.

2. An alarm circuit having a source of electrical power having a first side and a second side,

a normally open electrical switch having a pair of con ductors,

means for closing said switch under true-alarm conditions,

an electrically actuated warning device, having a first side connected to the first side of said power source and having a second side,

a pair of insulated wires, one said Wire being connected to said second side of said source and the other said wire being connected to the second side of said warning device, and

connection means for releasably connecting said first and second wires to said pair of conductors,

the combination therewith of:

an electrically conductive shunt electrode at said connection means interposed between said pair of wires on one hand and said pair of conductors on the other hand and spaced from said wires and conductors thereof and having a portion in between and spaced from them, and electrically connected to the first side of said power source so that should electrolyte be present at said connection means, said shunt electrode passes directly to power source such current as flows through said electrolyte rather than causing a short circuit between the pair of wires and thereby prevents false actuation of said warning device.

3. In an alarm circuit having a normally open electrical switch having a pair of conductors connected to a first connector,

means for closing said switch under true-alarm conditions,

a source of direct-current electrical power having one side grounded and a second side,

an electrically actuated warning device, grounded on one side and having a second side,

a pair of insulated wires connected to a second connector, said first and second connectors being joined to each other by a plug-socket-connection to each other, one said wire being connected to said second side of said source and the other said wire being connected to the second side of said warning device,

the combination therewith of:

an electrically grounded conductive electrode interposed in said plug-socket-connection between said two connectors and spaced from the conductors thereof and providing a web in between and spaced from said connectors, so that should electrolyte be present in said plug-socket-connection, said plate passes to ground such current as flows through said electrolyte rather than causing a short circuit between the pair of wires.

4. In a fire-alarm circuit having a temperature sensor,

-a normally open electrical switch closed by said sensor when said .sensoris subjected to a predetermined high temperature, said switch having a pair of telminals comprising a first connector,

a source of electrical power having first and second poles,

an electrically actuated warning device, connected on one side to said first pole, and having a second side, and

a pair of insulated wres connected to a second connector, said first and second connectors providing a plugsocket-connection to each other, one said wire being connected to said second pole and the other said wire being connected to said second side of said warning device,

the combination therewith of:

an electrically conductive shunt electrode interposed in said plug-socket-connection between said two connectors and having openings therethrough for spacing the metal of said plate from said terminals and wires .and having a portion in between said holes, said electrode being connected to said first pole for shunting to said power source any electrolytic short that may occur at said plug-socket-connection.

5. In a fire-alarm circuit having a temperature sensor,

a normally open electrical switch closed by said sensor when said sensor is subjected to a predetermined high temperature, said switch having a pair of terminals comprising a first connector,

a source of direct-current electrical power having two poles, one pole being grounded and the other pole ungrounded,

an electrically actuated warning device, grounded on one side, the other side being ungrounded, and

a pair of insulated wires connected to a second connector, said first and second connectors providing a plugsocket-connection to each other, one said wire being connected to the ungrounded pole of said source and the other said wire being connected to the ungrounded side of said warning device,

the combination therewith of:

an electrically grounded conductive shunt electrode interposed in said plug socket-connection between said two connectors and having openings therethrough for spacing the metal of said plate from said terminals and wires and providing a web in between said holes, for shunting to ground any electrolytic short that may occur at said plug-socket-connection.

6. A fire-alarm circuit including in combination:

a temperature sensor,

a normally open electrical switch closed by said sensor when said sensor is subjected to a predetermined high temperature, said switch having a pair of terminals and a conduct-or connected to each said terminal,

a first connector comprising a metal housing, said con and insulating means separating said conductors from each other and from said housing,

a source of direct-current electrical power having a first pole and a second pole, said first pole being connee-ted directly to said housing,

an electrically actuated warning device having a first side and a second side,

a circuit breaker connected to said second pole of said source,

a second connect-or having connection means mating with said first connector and providing therewith a plug-socket-connection.

an insulated wire connecting said second connector to said circuit breaker and through it to said second pole of said source,

an insulated and shielded wire connecting said second connector to said first side of said warning device, and

a conductive metal disc having two holes therethrough interposed in said plug-socket-conne-ction between said two connectors, the metal thereof being spaced from said conductors and wires thereof by said holes, said disc having a web in between said holes, said disc being electrically connected to said metal housing and serving to shunt to said power source any short that might be caused by electrolytic fluid in said plug-socket-connection to prevent actuation of sa d warning device thereby.

7. The circuit of claim 6 wherein said sensor has an electrically conductive housing, and having a sensor testing circuit connected to the end of said housing distant from said switch and a circuit breaker in series with said source, said sensor being connected near said switch to said first pole.

and including a shielded insulated line 8. A fire-alarm circuit including in combination:

a temperature sensor,

a normally open electrical switch closed by said sensor when said sensor is subjected to a predetermined high temperature, said switch having a pair of terminals and a conductor connected to each said terminal,

a first connector comprising a grounded metal housing, said conductors, and insulating means separating said conductors from each other and from said housing,

a source of direct-current electrical power having a grounded pole and a power pole,

an electrically actuated warning device having a grounded side and ungrounded side,

a circuit breaker connected to said power pole of said source,

a second connector having connection means mating with said first c0nnect0r and providing therewith a plug-socket-connection,

an insulated wire connecting said second connector to said circuit breaker and through it to said power pole of said source, v

an insulated and shielded Wire connecting said second connector to the ungrounded side of said warning device, and

a conductive metal disc having two holes therethrough interposed in said plug-socket-connection between said two connectors, the metal thereof being spaced from said conductors and wires thereof by said holes, said disc having a web in between said holes, said disc being electrically connected to said grounded metal housing and serving to ground any short that might be caused by electrolytic fluid in said plug- 8 socket-connection, thereby preventing false actuation of said warning device. 9. Thecircuit of claim 8 wherein said sensor has an electrically conductive housing, and having a sensor testing circuit connected to the end of said housing distant from said switch and including a shielded insulated line and a circuit breaker in series with said source and a ground for said sensor near said switch.

No references cited.

NEIL C. READ, Primary Examiner. 

3. IN AN ALARM CIRCUIT HAVING A NORMALLY OPEN ELECTRICAL SWITCH HAVING A PAIR OF CONDUCTORS CONNECTED TO A FIRST CONNECTOR, MEANS FOR CLOSING SAID SWITCH UNDER TRUE-ALARM CONDITIONS, A SOURCE OF DIRECT-CURRENT ELECTRICAL POWER HAVING ONE SIDE GROUNDED AND A SECOND SIDE, AN ELECTRICALLY ACTUATED WARNING DEVICE, GROUNDED ON ONE SIDE AND HAVING A SECOND SIDE, A PAIR OF INSULATED WIRES CONNECTED TO A SECOND CONNECTOR, SAID FIRST AND SECOND CONNECTORS BEING JOINED TO EACH OTHR BY A PLUG-SOCKET-CONNECTION TO EACH OTHER, ONE SAID WIRE BEING CONNECTED TO SAID SECOND SIDE OF SAID SOURCE AND THE OTHER SAID WIRE BEING CONNECTED TO THE SECOND SIDE OF SAID WARNING DEVICE, THE COMBINATION THEREWITH OF: AN ELECTRICALLY GROUNDED CONDUCTIVE ELECTRODE INTERPOSED IN SAID PLUG-SOCKET-CONNECTION BETWEEN SAID TWO CONNECTORS AND SPACED FROM THE CONDUCTORS THEREOF AND PROVIDING A WEB IN BETWEEN AND SPACED FROM SAID CONNECTORS, SO THAT SHOULD ELECTROLYTE BE PRESENT IN SAID PLUG-SOCKET-CONNECTION, SAID PLATE PASSES TO GROUND SUCH CURRENT AS FLOWS THROUGH SAID ELECTROLYTE RATHER THAN CAUSING A SHORT CIRCUIT BETWEEN THE PAIR OF WIRES. 